What is velocity?
Velocity is the rate of change of position in the same direction with respect to time.
When an object moves in a straight line from once position to another, its velocity is the distance travelled divided by the time taken for the move. It is measured in distance per time unit such as metres per second.
Velocity is a vector quantity which means that it has both magnitude and direction. The magnitude of a velocity is often referred to as speed.
If the direction of motion changes, the velocity changes. If a body is moving in an orbit its velocity is changing continuously as the direction of motion keeps changing. For example the Moon has an average speed of about 1 km/s, but its velocity changes continuously.